The present invention relates to a photoelectric receiver for camera equipment, especially for thermal-image equipment with local brightness adaptation, as well as to a method for local brightness adaptation.
From "Frankfurter Allgemeine Zeitung" of June 18, 1975, No. 137, an apparatus and method for the local brightness adaptation for television recording is known; see page 1 of the column "Natur und Wissenschaft". For this purpose, the picture is recorded by two cameras which scan the picture synchronously. The one of the two cameras is adjusted out-of-focus so that its signal corresponds to the average brightness of a small disc from the surroundings of the picture point proper. In special equipment, not described in detail, the signals of the two cameras are electronically compared, so that the brightness scale is adapted point by point to the prevailing illumination conditions. The contrast between two adjacent picture elements is thereby preserved without change, but, for instance, the dark portions of a scene can be emphasized in this manner over the brightly illuminated ones and be made visible more clearly. Overall, an increase of the dynamics is therefore achieved in the taking of pictures.
Since this method requires two complete picture pickup devices (e.g.: TV cameras), it is correspondingly expensive. Even more expensive would be such a method for thermal imaging equipment, the detectors of which require separate cooling devices.